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Question about OEM rear diff fluid

I’m coming up on 100k miles and am doing some preventative maintenance. I changed my diff fluid originally at around 65k miles and have some of the fluid from that change leftover. It has an expiration date on it of June 2017. So my question is, is this fluid still good to use? Since this fluid is about $30/bottle and you only need a little over one bottle I was thinking of buying one new bottle and using that entire bottle then just finishing off the fluid change with the old bottle. What do you guys think? Use the old fluid or stop being cheap and just buy two new bottles?

PS: the fluid I’m referring to is the ac delco fluid (part #92184900). It’s also been stored in a non insulated garage in TX since originally used.

I'd use it as long as the cap has been on. Seeing as the stuff can be in a diff, getting thoroughly sloshed around for thousands of miles before it's due to be changed, sitting in a bottle can't be that tough on it.

Being new to the forum, I really appreciate all of the available info. I am old and retired and still playing with cars and trucks. I just changed my differential fluid and will share experience. First, a real easy process with hardest part deciding on fluid. Went with the 92184900 fluid. My local GM dealer did not have the ZF Carbon specific fluid so I almost went with the regular stuff but info on this forum pointed to using the correct fluid's importance. I have rebuilt CHEVY post units where 100% of the clutch disc material had been dissolved by using the incorrect (synthetic) fluid. I bought my fluid from Amazon for about $22 a quart as I could not find it locally. One dealer told me the CHEVY dealership in Laurel, MS has six quarts but that is over 100 miles away. It is nice to have a drain plug!! With car on lift, process was easy. Old fluid was "carbon" black. Put 1.2 quarts of new in with an old suction gun I have had for longer than most members have lived and all is good. I would not hesitate to use old correct fluid in a closed container. I did not use additive and no chatter at this point. Still working on eliminating that "dad-gum" vibration that so many enjoy!